Objective:Electroacupuncture(EA)is an alternative treatment option for pain.Different frequencies of EA have different pain-relieving effects;however,the central mechanism is still not well understood.Methods:The Fos2A-iCreER(TRAP):Ai9 mice were divided into three groups(sham,2 Hz,and 100 Hz).The mice were intraperitoneally injected with 4-hydroxytamoxifen(4-OHT)immediately after EA at Zusanli(ST36)for 30 min to record the activated neurons.One week later,the mice were sacrificed,and the number of TRAP-treated neurons activated by EA in the thalamus,amygdala,cortex,and hypothalamus was determined.Results:In the cortex,2 Hz EA activated more TRAP-treated neurons than 100 Hz EA did in the cingulate cortex area 1(Cg1)and primary somatosensory cortex(S1),and 2 and 100 Hz EAs did not differ from sham EA.TRAP-treated neurons activated by 2 Hz EA were upregulated in the insular cortex(IC)and secondary somatosensory cortex(S2)compared with those activated by 100 Hz and sham EA.In the thalamus,the number of TRAP-treated neurons activated by 2 Hz EA was elevated in the paraventricular thalamic nucleus(PV)compared with those activated by sham EA.In the ventrolateral thalamic nucleus(VL),the number of TRAP-treated neurons activated by 2 Hz EA was significantly upregulated compared with those activated by 100 Hz EA,and sham EA showed no difference compared with 2 or 100 Hz EA.TRAP-treated neurons were more frequently activated in the ventral posterolateral thalamic nucleus(VPL)by 2 Hz EA than by 100 Hz or sham EA.Conclusions:Low-frequency EA ST36 effectively activates neurons in the Cg1,S1,S2,IC,VPL,PV,and VL.The enhanced excitability of the aforementioned nuclei induced by low-frequency EA may be related to its superior efficacy in the treatment of neuropathological pain.
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